Rotation of rotary tub of a washing machine during dehydration may go up to an order of 1000 rpm at maximum. To bring such high speed rotation to a halt in a short period of time, braking needs to be applied. One example of such braking is regenerative braking in which winding current, being opposite in phase to the induced voltage of motor, is generated by applying voltage delayed in phase relative to the induced voltage on motor windings. Electric power generated by regenerative braking is supplied to the DC (Direct Current) power supply circuit through diodes connected in reverse parallel to switching elements that constitute the inverter circuit. The supplied power charges the condensers constituting the DC power supply circuit to increase the DC voltage.
Under such configuration, the manner in which the increased DC voltage is controlled determines the measures taken in preventing circuit element breakdown, circuit size, and duration of braking. For instance, JP 2003-225493 A discloses a technology that eliminates the need of discharge resistors for consuming excess electric power by controlling the phase command of the energization signal and determining the voltage command based on the detected DC voltage.
In the field of washing machines, more and more models now come with a dry feature and some of such models incorporate a heat pump comprising a compressor to realize the dry feature. Such washer dryer is provided with a compressor motor for driving the compressor in addition to the washer motor for driving the rotary tub. Given such prerequisite configuration, a potential challenge to the industry may be a further efficient control of regenerative electric power.